Fluoropolymer films have long been used as a protective and decorative overlay for a variety of substrates such as metal, wood, and thermoplastic and thermoset polymers. With its excellent chemical resistance and weathering properties, a thin layer of fluoropolymer film can protect less durable substrates from damage in both exterior and interior use. In recent years, manufacturers of automobiles, recreational vehicles, sports craft and industrial and farm equipment have begun using decorative fluoropolymer film structures to surface selected parts of vehicles and equipment in lieu of paint. Single layer polymer film and multilayer polymer films have been used. Especially useful is a laminate of a pigmented resin layer and a clear resin layer which simulates a base coat/clear coat paint appearance. Film structures of this type are often referred to as “dry paint”. The use of dry paint is desirable since it avoids the need for solvents associated with conventional paint finishes. Dry paint films and laminates are especially useful for thermoformed polymeric parts, especially those with surface contours which are difficult to paint. Further, a dry paint surface allows manufacturers to use lower cost plastic substrates, which are not usable if painted by conventional means because of the unacceptable aesthetic finish that results.
Fluoropolymer films such as polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF) polymers and copolymers and blends of acrylic polymers and PVDF are often used as the decorative surface for dry paint due to their exceptional outdoor durability, chemical resistance and thermoformability. In the manufacture of parts finished with dry paint films, the film or laminate is often applied to a thermoplastic substrate which is then subjected to a thermoforming operation. A wide number of thermoplastic substrates are desirable for use such as polyolefins, polyesters, nylon, ABS, etc. However, forming a secure bond between fluoropolymer and such substrates is difficult. A bond is needed that will not delaminate after years of outdoor exposure. A manufacturing system for laminates of fluoropolymer films and thermoplastic substrates is also needed which is versatile enough to accommodate a variety of different thermoplastic materials and has a minimum number of processing steps.
U.S. Pat. No. 3,133,854 to Simms discloses a laminate structure of polyvinyl fluoride film with a variety of substrates such as metal, cellulose, cement, glass and polyvinyl chloride. The polyvinyl fluoride film is prepared by chemically activating the surface and the laminate is formed by using an intermediate layer of amine functional acrylic copolymer. However, for some thermoplastic substrates, the bond formed between the PVF layer and the substrate is weak and unsatisfactory. There is no teaching in Simms of bonding polyvinyl fluoride to polyolefin, polyamide, or polyester substrates.
U.S. Pat. No. 5,139,878 to Kim et al. discloses multilayer film structures of fluoropolymer film and thermoplastic polymer films using an intermediate adhesive layer of alkyl ester copolymers, modified polyolefins, or blends thereof. Kim's invention is aimed at producing packaging materials having good gas barrier properties and therefore the disclosure focuses on forming multilayer structures of chlorine containing fluoropolymer films adhered to polyester substrates. For some thermoplastic substrates and a number of fluoropolymer films, unsatisfactory bonds are formed using only the adhesive disclosed in this patent, especially if the laminate undergoes further forming steps.
Likewise, U.S. Pat. No. 4,585, 694 to Dehennau describes multilayer structures of vinyl or vinylidene fluoride polymer and alpha-olefin polymer bonded by the joint aid of vinyl acetate polymer and a copolymer of ethylene and vinyl acetate. Laminate film structures of this type possess unsatisfactory bonds which are subject to delamination especially when further forming steps are performed. Further such bonds are considered unsuitable for long lived outdoor use.